package twoPointers;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;

public class fourNums {
    public List<List<Integer>> fourSum(int[] nums, int target) {
        int n=nums.length;
        Arrays.sort(nums);
        List<List<Integer>> ret=new ArrayList<>();
        for(int i=0;i<n;){
            for(int j=i+1;j<n;){
                int left=j+1;
                int right=n-1;
                long aim=(long)target-nums[i]-nums[j];
                while(left<right){
                    int sum=nums[left]+nums[right];
                    if(aim>sum)left++;
                    else if(aim<sum)right--;
                    else{
                        ret.add(Arrays.asList(nums[i],nums[j],nums[left++],nums[right--]));
                        while(left<right&&nums[left]==nums[left-1])left++;
                        while(left<right&&nums[right]==nums[right+1])right--;
                    }

                }
                j++;
                while(j<n&&nums[j]==nums[j-1])j++;

            }
            i++;
            while(i<n&&nums[i]==nums[i-1])i++;
        }
        return ret;
    }
}
